Apparatus and method for electrically killing plants

ABSTRACT

An electrical energy processing unit of an apparatus to kill a plant or at least attenuate plant growth is disclosed. The electrical energy processing unit includes a converter and a control circuit. Also disclosed are an apparatus that includes the electrical energy processing unit and a method of utilizing the apparatus. Further disclosed are a computer program for a processor of the control circuit of the electrical energy processing unit and a non-transitory computer readable medium that includes the computer program.

CROSS REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCESTATEMENT

This application is a continuation of U.S. Ser. No. 16/803,548, filedFeb. 27, 2020; which is a continuation of U.S. Ser. No. 15/329,789,filed Jan. 27, 2017, now abandoned; which is a US national stageapplication filed under 35 USC § 371 of International Application No.PCT/GB2015/052168, filed Jul. 27, 2015; which claims priority toApplication NO. GB 1413435.7, filed Jul. 29, 2014; and Application No.GB 1505830.8, filed Apr. 4, 2015. The entire contents of theabove-referenced patents and patent applications are hereby expresslyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to electric apparatus that is configuredto attenuate plant growth by the application of electrical energythereto.

BACKGROUND

In properties both commercial and domestic it is common to kill or atleast control the growth of unwanted plants, commonly referred to asweeds. A conventional process for doing so is to extract manually or bymeans of a mechanical implement, the weed from the ground. It ispreferable to extract the weed in its entirety with its roots intact, asa portion that remains in the ground can re-grow. A drawback with such aprocess is that ensuring entire extraction is laborious and particularlydifficult. A further drawback is that weeds can seed or re-grow quickly,particularly in warm and wet climates, which means that regularrepetitions of the process are required. A yet further drawback is thatmechanically removing a weed can disturb the surrounding soil such that:buried seeds are surfaced; crops/seeds are inadvertently removed via theinterconnecting soil of the weed that is removed with the weed; the soilis subject to nutrient and moisture loss.

A solution to the above drawbacks is the process of chemically poisoningthe weed by means of a pesticide or more particularly a herbicide.Desirably, herbicides can be formulated to selectively target specificweeds whilst leaving a desired crop relatively unharmed. Such herbicidesmay function by interfering with the growth of the weed and are oftensynthetic mimics of natural plant hormones. Exposure of herbicides tohumans and animals can arise as a result of improper application, forexample, contact during application or as a residue on foodstuffs orother contamination of the food chain. Such exposure is undesirablesince a known drawback with herbicides is that they can be toxic tohumans and animals. More particularly, herbicides can cause varioushealth problems such as skin and respiratory conditions. There are alsoconcerns over carcinogenicity (e.g. Triazine and Phenoxy herbicides) aswell as a relationship with Parkinson's disease. A further drawback isthat herbicides are not always successful in killing the target weeds. Ayet further drawback is that herbicides can be washed off plants if rainfollows their application or blown away due to wind thereby restrictingthe times of application. A yet further drawback is that herbicides canbe harmful to the surrounding environment, for example, they can betransported via leaching or surface runoff to contaminate groundwater ordistant surface water sources. Transport of herbicides is promoted byintense rainfall and soils with limited absorption and retention. Theseeffects are confounded if the particular herbicide has high persistence(resistance to degradation) and water solubility. As a result of thesenumerous drawbacks there are increasingly severe restrictions on the useof herbicides, particularly throughout the European Union. Moreover, asa result of these numerous drawbacks consumers are increasinglydemanding organic produce, for which the use of herbicides isprohibited.

A solution to the above drawbacks is the process of killing the weed bymeans of the application of electrical energy thereto. Apparatus used insuch a process generally comprise: an electrical energy source that isarranged with a high-voltage side in electrical contact with applicatorelectrodes; the applicator electrodes configured to transfer thehigh-voltage to the weed; a low-voltage side of the electrical energysource connected to ground thus completing a circuit whereby the loadcomprises a current drawn through the weed. Advantageously, such aprocess does not contaminate the environment to the same extent as aherbicidal process nor is it as toxic to humans and animals.

U.S. Pat. No. 4,338,743 discloses such apparatus, wherein the electricalenergy source comprises an engine-generator and a high-voltagetransformer. The generator supplies electrical current to a primarywinding of the high-voltage transformer, the high-voltage transformerhas a secondary winding electrically connected to applicator electrodes.The applicator electrodes are configured for direct transmission of thehigh-voltage to weeds. The apparatus is for agricultural use and isdisposed on a vehicle that can be towed by an agricultural vehicle. Theapparatus functions in a first mode: wherein the high-voltage is appliedto the applicator electrodes or in a stand-by mode: wherein electricalenergy is supplied from the generator to electrical outlets that can beused to supply other agricultural equipment. The apparatus is operableto generate 14.4 kV at 60±5 Hz at the applicator electrodes. A drawbackwith this apparatus is that the high-voltage transformer is bulky. Afurther drawback is that the output at the applicator electrodes isparticularly dangerous to humans and animals.

U.S. Pat. No. 5,600,918 discloses further such apparatus, wherein theelectrical energy source comprises a piezoelectric crystal and anactuator. The actuator is configured to apply a compressive force to thepiezoelectric crystal to thereby generate a high-voltage that iselectrically connected to the applicator electrodes. The apparatus isoperable to generate 50-1500 V in short bursts at the applicatorelectrodes. Advantageously, the apparatus does not require a bulkytransformer, however it is limited to non-agricultural applications dueto the particularly limited power the piezoelectric crystal can supply.

A solution to some of the drawbacks of the above apparatus is providedin JP 2002360151, which discloses a yet further such apparatus, whereinthe electrical energy source comprises a battery that supplies a directcurrent of 24 V to an oscillating unit and a high-voltage transformer.The oscillating unit outputs an oscillating signal to transistors thatswitch with the oscillating signal to effect the switching of a currentthrough a primary coil of the high-voltage transformer. The high-voltagetransformer is configured such that the voltage over a secondary coil isstepped-up to 6 kV with a frequency of 15 kHz and a low current of 0.5mA. The secondary coil is electrically connected to an electrode thatcomprises a dielectric outer layer. The apparatus is configured to causecorona discharge at the leaves of the weed and yield ozone that acts tochemically poison the weed. Due to the particular low current the bodyof the weed is generally not targeted. Accordingly, the apparatus is ingeneral limited to the treatment of small areas and is therefore notsuitable for agricultural use.

A further solution to some of the drawbacks of the above apparatus isprovided in JP H3-83534, and the related publication: ‘Destruction ofWeeds by Pulsed High-Voltage Discharges’, A. Mizuno, T. Tenma and N.Yamano, Toyohashi University of Technology, 1990, wherein the electricalenergy source comprises a DC electrical source and a capacitor. Thecapacitor is sequentially: connected to the DC electrical source andcharged; disconnected from the DC electrical source; connected to anapplicator electrode and discharged therefrom as a spark. The applicatorelectrode transmits the generated spark through the air to the nearestweed, i.e. without direct contact between the weed and electrode.Accordingly the apparatus is not configured for direct contact betweenthe applicator electrode and the weed. The spark comprises 15 kV at 30pulses per second. A drawback with this apparatus is that the path ofthe spark is potentially unpredictable due to arcing and therefore couldbe transmitted to nearby humans and animals. A further drawback is thatsince the voltage is particularly high there is a significant risk ofinjury from high current transfer. A yet further drawback is that thereis a risk of fire due to ignition of the weed/surrounding plants. A yetfurther drawback is that the use of a capacitor in this way generallylimits the apparatus to the treatment of small areas and small weeds:the apparatus it is therefore not particularly suitable for agriculturaluse.

A yet further solution to some of the above drawbacks of the aboveapparatus is provided in the publication: ‘A Portable Weed ControlDevice using High Frequency AC Voltage’, A. Mizuno, A. Nagura, T.Miyamoto and A. Chakrabarti, Toyohashi University of Technology, 2001,wherein an electrical energy source comprises a DC electrical sourcethat supplies a direct current of 12V to an oscillating circuit and ahigh-voltage transformer. The oscillating circuit outputs an oscillatingsignal to effect the switching of a current through a primary coil ofthe high-voltage transformer. The high-voltage transformer is configuredsuch that the voltage over a secondary coil is stepped-up to 3 kV with afrequency of 12.5 kHz. The secondary coil is electrically connected toan applicator electrode, which is in electrical contact with a weed. Adrawback with this apparatus is that high-voltage output at theapplicator electrodes is still particularly dangerous to humans andanimals. A further drawback is that the apparatus is in general limitedto the treatment of small areas and is therefore not suitable foragricultural use.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how embodimentsof the same may be carried into effect, reference will now be made byway of example to the accompanying diagrammatic drawings in which:

FIG. 1 is a block diagram of electrical weed killing apparatus accordingto the invention;

FIG. 2 is a block diagram of a first embodiment of an electrical energysource of the apparatus of FIG. 1 ;

FIG. 3 is an illustrative diagram of a second embodiment of theelectrical energy source of FIG. 1 ;

FIG. 4 is an illustrative diagram of a first embodiment of an applicatorunit of the apparatus of FIG. 1 ;

FIG. 5 is an illustrative diagram of a second embodiment of theapplicator unit of FIG. 1 ;

FIG. 6 is an illustrative diagram of an earth unit of the electricalweed killing apparatus of FIG. 1 .

FIG. 7 is a block diagram showing an embodiment of an electrical energyprocessing unit of the apparatus of FIG. 1 ;

FIG. 8 is a block diagram showing an embodiment of a control circuit anda converter of the electrical energy processing unit of FIG. 7 ;

FIG. 9 is a schematic diagram showing an embodiment of a converter ofthe electrical energy processing unit of FIG. 7 ;

FIG. 10 is a schematic diagram of a first embodiment of the electricalenergy processing unit of FIG. 1 ;

FIG. 11 is a schematic diagram of a second embodiment of the electricalenergy processing unit of FIG. 1 ;

FIG. 12 a is an illustration of a waveform signal and a correspondingprocessed electrical energy output from the first embodiment of theelectrical energy processing unit, and FIG. 12 b is an illustration of awaveform signal and a corresponding processed electrical energy outputfrom the second embodiment of the electrical energy processing unit;

FIG. 13 is a schematic diagram of a third embodiment of the electricalenergy processing unit of FIG. 1 ;

FIG. 14 is a schematic diagram of a fourth embodiment of the electricalenergy processing unit of FIG. 1 ;

FIG. 15 is an illustration of the electrical weed killing apparatus ofFIG. 1 adapted for use in an agricultural environment;

FIG. 16 shows tabulated experimental results from electrical weedkilling apparatus according to the invention.

DETAILED DESCRIPTION

An object of the invention is to provide apparatus to electricallycontrol plant growth that is effective such that it may replaceherbicides and/or physical extraction in a range of environments, i.e.:agricultural; commercial (e.g. on sports fields, golf courses); privatenon-commercial (home use).

An object of the invention is to provide apparatus to electricallycontrol plant growth that is relatively safe to use.

It would be advantageous to provide apparatus to electrically controlplant growth that is cost-effective to manufacture.

It would be advantageous to provide apparatus to electrically controlplant growth that is compact.

It would be advantageous to provide apparatus to electrically controlplant growth that is convenient to use.

It would be advantageous to provide apparatus to electrically controlplant growth that can quickly control plant growth.

Objects of the invention are achieved by: the electrical energyprocessing unit according to claim 1; the apparatus according to claim9; the method according to claim 14; the use according to claim 16; thecomputer program according to claim 17.

Disclosed herein and according to a first aspect of the invention is anelectrical energy processing unit of apparatus to electrically controlplant growth, the electrical energy processing unit comprising: aconverter configured to receive unprocessed electrical energy from anelectrical energy source, to convert the unprocessed electrical energyto processed electrical energy and to output said processed electricalenergy to an applicator unit. Typically the converter is configured totransmit the said processed electrical energy between an applicatorelectrode of an applicator unit and an earth electrode of an earth unit.More particularly converter may be configured to transmit the processedelectrical energy through a processed electrical energy circuit. Theprocessed electrical energy circuit may comprise: an applicatorelectrode of an applicator unit; an earth electrode of an earth unit; inuse a treated plant and the ground. The electrical energy processingunit may comprise a control circuit operable to control the converter toconvert the unprocessed electrical energy to the processed electricalenergy. In an example wherein the converter provides a fixed operationon the unprocessed electrical energy it will be appreciated that acontrol circuit is not required. However, generally the electricalenergy processing unit comprises a control circuit when control of thesaid converter is required, e.g. to provide a varying output of anaspect, (e.g. voltage, current or power) of the processed electricalenergy. The processed electrical energy is suitable for killing a plantor at least partially attenuating plant growth. The processed electricalenergy comprises a waveform, which can have a repeating unit variousshapes, with a frequency of at least 18 kHz. The processed electricalenergy may have a peak voltage of above 1 kV or more particularly withinone of the following ranges: 1 kV to 30 kV; 2 kV to 20 kV; 2.5 kV to17.5 kV. The peak voltage is defined as the peak amplitude of therepeating units of the waveform. The frequency is defined as the numberof repeating units of the waveform per unit time. A repeating unit isdefined as a unit that repeats with substantially the same form, e.g. itmay comprise waveforms of substantial the same shape including when theamplitude and/or duty cycle or period is adjusted for control of theprocessed electrical energy.

Advantageously, objects of the invention are solved since processedelectrical energy that comprises a waveform with a frequency of at least18 kHz or more particularly of at least: 20 or 25 or 30 or 35 or 40 or50 kHz is less of a safety risk to humans and animals than the apparatusof the prior art, which operate outside this frequency range. In moredetail, it has been found that for electrical current above suchfrequencies the nerve and muscle tissue systems of humans and animals donot have time to react to the current. In more detail, the said nervesystems have transport mechanisms that comprise chemical iontransmission across a cell membrane. Said transport mechanisms occurover a finite amount of time, referred to as a chronaxia, e.g. thechronaxia of a nerve cell may be 0.1-10 ms. For electrical frequenciesin the said range it has been found that the electrical shock ceases tobecome apparent and the nerve system may not respond in a substantiallydetrimental manner.

Moreover, objects of the invention are solved since a processedelectrical energy that comprises a waveform with a frequency of at least18 kHz or more particularly of at least: 20 or 25 or 30 or 35 or 40 or50 kHz is believed to be effective at controlling plant growth than theapparatus of the prior art, which operate outside this frequency range.In particular it is believed that plants tend to conduct the saidhigh-frequency current through their outer layers, with damage being byheat to the said conducting layers. In a stem of a plant the outerlayers comprise: xylem; phloem; sclerenchyma; cortex; epidermis, whereasthe inner layers comprise the protoxylem and pith. It is believed thatthe high-frequency current is in particular concentrated in the xylemand/or phloem that comprise the living tissue of the plant for thetransportation of water and other nutrients. Accordingly, they arecritical to the plant and are more specifically targeted by the currentin the claimed high-frequency range.

The electrical energy processing unit is configured to produce processedelectrical energy to kill a plant (e.g. immediate destruction of theplant such that the plant does not grow back) or at least attenuate thegrowth of a plant (e.g. such that the natural growth of a plant issubstantially reduced). The electrical energy processing unit isconfigured to produce processed electrical energy that has an initialcurrent of at least 10 mA or 50 mA or 100 mA or 500 mA (rms or peak).The current is sufficient for substantial damage of the body, i.e. thestem of the plant as it travels therethrough. The electrical energyprocessing unit is configured to produce processed electrical energythat has a power (i.e. the initial power when first applying theelectrical energy to a plant) of at least 5 W or 10 W or 50 W or 100 W.The electrical energy processing unit is configured to produce processedelectrical energy that is operable to kill a plant or at least partiallyattenuating plant growth with a treatment time of at least 10 or 100milliseconds. The maximum frequency may be 5 MHz or 2 MHz or 1 MHz or500 kHz or 350 kHz or 100 kHz or 75 kHz or 50 kHz or 40 kHz or any valuetherebetween.

The abovementioned minimum and maximum frequency ranges may be combinedin any manner (i.e. such that the maximum frequency is greater than theminimum frequency). The preferred frequency range may for example beselected as 18 kHz-500 kHz or 20 kHz-100 kHz or 30 kHz-50 kHz. It willbe appreciated that as the frequency is increased, i.e. from 18 kHz, theabovementioned effects increase.

Advantageously, by configuring the electrical energy processing unit tooperate at the said high-frequency range it can be made particularlycompact since suitable high-frequency components are generally morecompact than those that are configured to operate at a low-frequency.

The processed electrical energy may comprise a periodic or aperiodicwaveform, i.e. a waveform that continuously repeats with the repeatingunits therein having a constant or a varying period, e.g. a pulsed wavewith a fixed duty cycle or a varying duty cycle. The shape of therepeating unit may be one of or a combination of one or more of thefollowing forms: sine wave; saw-tooth wave; triangular wave; squarewave; pulsed, e.g. DC pulsatile, half-wave rectified; other known form.The exact shape of the repeating unit may be an approximation of one ofthe aforesaid forms for reasons of distortion, e.g. overshoot/undershootand the associated ringing and settle time. The repeating unit may bepositive or negative or a combination thereof with respect to areference value, which is typically 0 V.

The control circuit generally controls the converter by means of acontrol signal. The form of the processed electrical energy maygenerally correspond to that defined by the control signal (e.g. an ACor DC waveform) but may be an approximation thereof for reasons ofdistortion.

The control aspect of the control circuit may be a simple function, e.g.on/off of the processed electrical energy e.g. for an electrical energyprocessing unit configured to produced processed electrical energy of afixed waveform. In a more sophisticated example the control aspect maybe the control of one or more of a list comprising the following aspectsof the waveform of the processed electrical energy: form; duty cycle,which is typically in the range of 0.05-0.45 (e.g. for a pulsedwaveform); on/off; amplitude (e.g. to maintain the peak voltage at aparticular magnitude for varying load); frequency; period; current;power; shape; other aspect.

The control circuit is preferably configured to control the aspect ofthe processed electrical energy, which is generally one or more of the:voltage; current; power. The control circuit may be configured tocontrol the aspect to be: maintained substantially at a predeterminedvalue; and/or below or above a predetermined value (e.g. a different tothe substantially maintained predetermined value); and/or within aparticular range, which is determined by a first and secondpredetermined value (e.g. the first and second predetermined values aredifferent to each other, and may be different to the aforesaidpredetermined values). The control is generally for the said aspect ofthe processed electrical energy through or over a load as the loadvaries during treatment, whereby the load comprises a current drawnthrough a treated plant.

Substantially at a predetermined value may be defined as being ±1 or 2.5or 5% of a particular value of the aspect. In the configuration whereinthe aspect is voltage the particular value may for example be 5 or 10 kV(e.g. the peak or rms voltage). In the configuration wherein the aspectis current the particular value may for example be 0.1 or 0.5 A (e.g.the peak or rms current). In the configuration wherein the aspect ispower the predetermined value may for example be 500 or 1000 W.

Below or above a predetermined value can simply delimit the maximum orminimum value of the aspect. In the configuration wherein the aspect isvoltage the predetermined value may for example be 5 or 10 kV (e.g. thepeak or rms voltage), such that this value is either not exceeded or setas the minimum. In the configuration wherein the aspect is current theparticular value may for example be 0.1 or 0.5 A (e.g. the peak or rmscurrent), such that this value is either not exceeded or set as theminimum. In the configuration wherein the aspect is power thepredetermined value may for example be 500 or 1000 W such that thisvalue is either not exceeded or set as the minimum. The maximum orminimum value may alternatively be defined as ±5 or 15 or 20 or 25% of anominal value, e.g. the aforesaid voltage, current or power values.

Within a particular range defined by a first and second predeterminedvalue simply delimit the maximum and minimum value of the aspect. In theconfiguration wherein the aspect is voltage the first predeterminedvalue may for example be 5 kV and the second predetermined value may forexample be 10 kV (e.g. the peak or rms voltage), such that the voltageis maintained at above 5 kV and below 10 kV. In a similar fashionexample values of 0.1 or 0.5 A (e.g. the peak or rms current) and 500 or1000 W can be used for current and power. The first and secondpredetermined value may alternatively be defined as ±5 or 15 or 20 or25% of a nominal value, e.g. the aforesaid voltage, current or powervalues.

The control circuit may be configured to control one or more of theaforesaid aspects by controlling an amplitude and/or duty cycle orperiod of the processed electrical energy. Such control may be open loopor closed loop control using the converter feedback signal.

In the configuration wherein the said aspect is the voltage, the controlcircuit may be configured to: in response to a decreasing voltage (e.g.the peak or rms voltage) of the processed electrical energy increase theamplitude and/or duty cycle or period thereof; and/or in response to anincreasing voltage of the processed electrical energy decrease theamplitude and/or duty cycle or period thereof. In the configurationwherein the said aspect is the current or power, the control circuit maybe configured to: in response to a decreasing current (e.g. the peak orrms current) of the processed electrical energy increase the amplitudeand/or duty cycle or period thereof; and/or in response to an increasingcurrent of the processed electrical energy decrease the amplitude and/orduty cycle or period thereof.

The control circuit may be configured allow the said aspect to initiallyincrease from a first value to a second value, wherein when achievingthe second value the said aspect is controlled in the one of theaforesaid manners. As an example of this configuration of control: inthe configuration wherein the aspect is voltage the first value may forexample be 2 kV and the second value may be 5 kV, wherein when 5 kV isachieved the control is implemented, e.g. to: maintain the voltagesubstantially at 5 kV or be ±20% of 5 kV or if the voltage decreasesfrom 5 kV the duty cycle or period and/or amplitude of the processedelectrical energy is increased.

The converter may comprise at least one sensor, the control circuitbeing operatively connected to the sensor to receive therefrom aconverter feedback signal, the converter feedback signal comprisinginformation to monitor the processed electrical energy. The sensor(s) ofthe converter may be a voltage sensor and/or a current sensor and thecorresponding converter feedback signal may comprise voltage and/orcurrent information.

The control circuit may be configured to provide open-loop control ofthe said one or more aspects of the output processed electrical energy.Alternatively, the control circuit may be configured to provideclosed-loop control of the said one or more aspects of the processedelectrical energy using the said converter feedback signal. The saidcontrol of the processed electrical energy is typically via control ofthe waveform signal e.g. via a control of the waveform generation unitand other associated units when present.

The control circuit may further be operable to control operation of oneor more of the; applicator unit; earth unit; electrical energy source,e.g. by an electrical energy source feedback and control signal.

Typically the control circuit comprises a processor, e.g. to output thesaid control signal to control the converter. The processor generallyprovides the aforesaid control of the processed electrical energy. Thecontrol circuit may further comprise a user interface operably connectedto the processor for control of the operation of the processor and/orfor monitoring of the operation of one of more of a list comprising thefollowing: electrical energy processing unit; applicator unit; earthunit; electrical energy source. Alternatively, there is no userinterface, e.g. the control circuit is operated automatically inresponse to an applied current from the electrical energy source.

The converter is configured to convert the unprocessed electrical energyto the desired form of processed electrical energy e.g. via conversionone or more of the: voltage; current; frequency; other optional aspectsof the waveform.

The converter may comprise a converter unit which may have variousconfigurations depending on its mode of operation, e.g.: the converterconverts only frequency (e.g. the unprocessed electrical energy issupplied at the desired voltage) and the converter unit comprises anelectrically operated chopper switch, the switch arranged in series withthe unprocessed electrical energy; the converter converts only voltage(e.g. the unprocessed electrical energy is supplied at the desiredfrequency) and the converter unit comprises a variable or non-variabletransformer. In further examples the converter unit may comprise acharge pump or boost converter or other suitable electrical component.

Generally energy the converter increases the voltage and applies thedesired frequency, e.g. the unprocessed electrical energy is of a lowervoltage than the processed electrical energy and has a direct current.In such an example the control circuit of the electrical energyprocessing unit may comprise a waveform generation unit and a processor.The waveform generation unit is configured to generate a control signalcomprising a waveform signal, e.g. the processor is configured tocontrol the converter via the waveform generation unit (and otherassociated components when present). The waveform signal generallycomprises a non-steady AC or DC signal that is representative of thewaveform of the processed electrical energy, e.g. is it amplified by theconverter to derive the required form of the processed electricalenergy. The waveform of the waveform signal may be controlled by theprocessor in terms of its: form; duty cycle, which is typically in therange of 0.05-0.45 (e.g. for a pulsed waveform); on/off; amplitude (e.g.to maintain the peak voltage at a particular magnitude for varyingload); frequency; period; current; power; shape; other aspect, e.g. tocontrol the processed electrical energy in one of the aforesaid manners.The processor and waveform generator may be an integrated unit, e.g. anintegrated circuit or separate units in communication via a controlsignal. Generally the waveform generation unit is part of the aforesaidcontrol circuit that comprises the processor. However, waveformgeneration unit may comprise an electronic component operable togenerate a fixed waveform output, e.g. with no input other than anelectrical energy supply. For example it may comprise any suitablesignal generator that may be arranged as an integrated circuit. In suchan example the processor may be obviated. In such an example theconverter may comprise a switching unit and a converter unit. Theswitching unit may comprise one or more electrically operated switch,the said switch to receive the control signal and to switch therewiththe unprocessed electrical energy. The electrically operated switch canbe a transistor or a triac or other suitable component. In such anexample the converter unit may comprise a transformer. The transformermay be arranged with the switched unprocessed electrical energy througha primary winding thereof and the processed electrical through asecondary winding thereof. In such an example the converter unit maycomprise another suitable electrical component such as a charge pump orboost converter.

Disclosed herein according to a second aspect of the invention isapparatus to electrically control plant growth comprising the electricalenergy processing unit according to any feature of the first aspect andat least one applicator unit to apply the processed electrical energy toa plant. The applicator unit may comprise an applicator electrode. Theapplicator electrode may comprise an electrically conductive material(e.g. a material with high electrical conductivity, such as a metal andnot a dielectric material), which is connected to the converter of theelectrical energy processing unit to receive therefrom the processedelectrical energy. The applicator electrode is preferably configured fordirect transmission of the processed electrical energy to a plant, e.g.a substantial portion of the applicator electrode is exposed so that itcan touch a plant for the direct transmission of the processedelectrical energy thereto. The applicator electrode may alternatively beconfigured for transmission of the processed electrical energy to theplant by arcing, i.e. spark transmission, without directly touching theplant (e.g. it has associated therewith an insulating housing to preventdirect contacting between the electrode and plant).

The applicator electrode of the applicator unit may further comprise adielectric material, which is arranged with the processed electricalenergy transmitted through (e.g. substantially or fully through) thesaid dielectric material to a treated plant (e.g. transmission is in theorder of: electrically conductive material; dielectric material; plant).The dielectric material is preferably operable to conduct the processedelectrical energy by capacitive action. The dielectric material maycomprise a layer or coating on the electrically conductive material,e.g. on an exposed outer surface thereof. The dielectric material mayhave a thickness of at least 0.1 or 0.5 or 1 mm. The dielectric materialmay have a maximum thickness less than or equal to 2 or 5 or 10 mm.

The apparatus to electrically control plant growth may further comprisean earth unit comprising an earth electrode. The earth electrode maycomprise an electrically conductive material (e.g. a material with highelectrical conductivity, such as a metal and not a dielectric material),which is connected to the converter to receive the processed electricalenergy transmitted from the applicator unit through a load comprising aplant. The earth unit completes a current path comprising the:electrical energy source; electrical energy processing unit; applicatorunit; treated plant; ground; earth unit; electrical energy processingunit; electrical energy source. The earth electrode may be configured toreceive the high voltage electrical energy when inserted into theground. Alternatively, the earth electrode may be configured to receivethe high voltage electrical energy when resting on a surface of theground, i.e. to maintain electrical continuity between the ground andthe earth electrode when resting on the surface of ground, e.g. suchthat the processed electrical energy transmitted from the applicatorunit to a plant and into the ground can be transmitted from the groundto the earth unit without the earth unit needing to be inserted into theground. Preferably, the earth electrode is configured to maintainelectrical continuity with the ground whilst being moved along theground, e.g. by sliding or rolling as part of a rotary member. Typicallyan earth electrode of this type is configured to have a substantiallyflat surface to abut the ground, e.g. with a surface area of at least 5or 10 or 20 or 50 cm², e.g. as a plate. Typically an earth unit of thistype is for use when the frequency of the processed electrical energy isabove 20 or 25 or 40 or 50 or 75 or 100 kHz.

The earth electrode of the earth unit may further comprise a dielectricmaterial, which is arranged with the processed electrical energy beingtransmitted through (e.g. substantially or fully through) the saiddielectric material to the electrically conductive material (e.g.transmission is in the order of: plant; dielectric material;electrically conductive material). The dielectric material is preferablyoperable to conduct the processed electrical energy by capacitiveaction. The dielectric material may comprise a layer or coating on theelectrically conductive material, e.g. on an exposed outer surfacethereof. The dielectric material may have a thickness of at least 0.1 or0.5 or 1 mm. The dielectric material may have a maximum thickness lessthan or equal to 2 or 5 or 10 mm.

The apparatus to electrically control plant growth may comprise anelectrical energy source connected to the electrical energy processingunit and/or means for connecting an electrical energy source to theelectrical energy processing unit (e.g. a plug). The electrical energysource may comprise one of the electrical energy sources selected fromthe following: engine-generator; battery; fuel cell; mains electricalsupply; vehicle power take-off shaft driving a generator. The electricalenergy source (as in the aforementioned examples) may be a portable(e.g. the battery) or external source (e.g. an AC line supply). Themeans for connecting may comprise part of an electrical interface, e.g.a plug.

Disclosed herein according to a third aspect of the invention is amethod of electrically controlling plant growth comprising: supplyingprocessed electrical energy to a plant using the apparatus toelectrically control plant growth according to any feature of the secondaspect, wherein the processed electrical energy comprises a waveform,which can have a repeating unit various shapes, with a frequency of atleast 18 kHz and with a peak voltage of at least 1 kV or other saidfrequency and voltage range.

The method may further comprise controlling an aspect of the processedelectrical energy. The said aspect may be controlled by controlling anamplitude and/or duty cycle or period of the processed electricalenergy. The said aspect may be one or more of the: voltage; current;power. The control may be open loop or closed loop using the converterfeedback signal. The method may further comprise controlling the saidaspect to be: maintained substantially at a predetermined value; orbelow or above a predetermined value; or within a particular range,which is determined by a first predetermined value and second differentpredetermined value.

The method may comprise using the apparatus to electrically controlplant growth that comprises the earth unit comprising the aforesaidearth electrode that is configured to receive the high voltageelectrical energy when resting on a surface of the ground (e.g. arrangedplanar to the ground, e.g. without insertion into the ground) to:electrically control the growth of a first plant located at a firstlocation and a second plant located at a second location by: moving theearth electrode of the earth unit along the ground whilst maintainingelectrical continuity between the earth unit and the ground, e.g.electrical continuity is maintained without the need to insert theelectrode of the earth unit into the ground. The applicator unit can bemoved between operational proximity of the first location andoperational proximity of the second location whilst moving the earthelectrode of the earth unit resting substantially on the ground betweenoperational proximity of the first location and operational proximity ofthe second location.

The method may comprise establishing a threshold voltage. The method maycomprise determining a treatment time. The threshold voltage andtreatment time may be determined from experimental data, (e.g. adatabase) and/or predicted (e.g. based on relevant experimental data).

Disclosed herein according to a fourth aspect of the invention is theuse of an electrical energy processing unit according to any feature ofthe first aspect for treating a plant to kill or at least attenuategrowth thereof.

Disclosed herein according to a fifth aspect of the invention is acomputer program for a processor of a control circuit of apparatus toelectrically control plant growth according to any feature of the secondaspect, the computer program comprising program code to control (e.g.when executed) the converter (e.g. via a waveform generation unit or viadirect control thereof) to generate processed electrical energy with awaveform that has a frequency of at least 18 kHz and with a peak voltageof at least 1 kV. The program code may be for programing of theprocessor, e.g. for upload onto a memory unit thereof or for programingof programmable logic of the processor.

The computer program may further comprise program code to: control anaspect of the processed electrical energy. The said aspect may becontrolled by controlling an amplitude and/or duty cycle or period ofthe processed electrical energy. The said aspect may be one or more ofthe: voltage; current; power. The control may be open loop or closedloop using an input converter feedback signal. The computer program mayfurther comprise program code to: control the said aspect to bemaintained substantially at and/or below and/or above a predeterminedvalue and/or within a particular range, the range being determined by afirst and second predetermined value. Other features controlled by theprogram code of the computer program include those of the first andsecond aspect.

Disclosed herein according to a sixth aspect of the invention is anon-transitory computer readable medium comprising the computer programaccording any feature of the fourth aspect. The non-transitory computerreadable medium may comprise a memory unit of the processor or othercomputer-readable storage media for having computer readable programcode stored thereon for programming a computer, e.g. a hard disk, aCD-ROM, an optical storage device, a magnetic storage device, Flashmemory.

Disclosed herein according to a seventh aspect of the invention isprovided a computer implemented method for implementing the methodassociated with the computer program of the fifth aspect. The aboveaspects of the invention may be combined in any suitable combination.Moreover, various features herein may be combined with one or more ofthe above aspects to provide combinations other than those specificallyillustrated and described. Further objects and advantageous features ofthe invention will be apparent from the claims, from the detaileddescription, and annexed drawings.

The following describes a single general embodiment apparatus to whichthe various described embodiment features can be added withoutlimitation, including those described in the summary of invention.

FIG. 1 shows a block diagram of an exemplary abstraction of electricalapparatus 2 to control plant growth according to the invention. Theapparatus 2 can be suitably adapted for applications wherein large areasof plants are required to be treated, for example, applications in anagricultural environment or commercial environments (such as golfcourses or sports pitches). Equally, it can be adapted for applicationswherein smaller areas of plants are required to be treated, for example,private non-commercial use in the treatment of a garden of a home user.The apparatus 2 may be considered to comprise at a first level thereof:an electrical energy source 4; a processed electrical energy circuit 20;an electrical energy processing unit 6, which are describedsequentially.

Electrical Energy Source

The electrical energy source 4 is operable to provide unprocessedelectrical energy to the electrical energy processing unit 6 forconversion to processed electrical energy 36. The unprocessed electricalenergy 34 may comprise any kind of electrical energy, such as a: directcurrent (DC), e.g. 12 V-24 V; or an alternating current (AC), e.g. 110Vrms-240 Vrms at 50-60 Hz. The electrical energy source 4 may be fullyor partially controlled by the electrical energy processing unit 6 e.g.by means of open-loop control or by means of closed-loop control, whichcomprises using an electrical energy source feedback and control signalto control and monitor aspects of the unprocessed electrical energy 34,e.g. the voltage and/or current and/or frequency by means of sensors,which is discussed in more detail further on. Alternatively theelectrical energy source 4 has a separate control system, whichcomprises a user interface, such as actuators and/or a dedicated controlsystem. The electrical energy source 4 can be arranged integrated withor discrete from the electrical energy processing unit 6. Moreover, theelectrical energy source 4 may be arranged to supply one or moreelectrical energy processing units 6, which are commonly orindependently controlled. Accordingly, it will be appreciated that theelectrical energy source 4 may comprise various means, examples of whichare discussed following.

In FIG. 2 shows in block form a preferred first embodiment of theelectrical energy source 4, which is applicable to agricultural or homeenvironments. Herein an engine-generator comprises an internalcombustion engine 10 and an electro-magnetic generator 12. The engine 10provides rotational energy to a rotor of the generator 12 that isconfigured to convert the rotational energy in to the unprocessedelectrical energy 34, which is in turn supplied to the electrical energyprocessing unit 6.

The engine-generator further comprises controls 14 operable to controlas input the engine 10 and/or generator 12. For example, the controls 14may be operable to control one or more of the following inputoperational parameters of the engine 10: start-up/shut-down; angularvelocity (of the rotor or engine); other operational parameters such aschoke, and a disconnect switch of the generator 12. The controls 14 maycomprise manual (for example, actuators) and/or automated means (forexample, electrically operated actuators). Automated controls 14 arepreferably controlled by the electrical energy processing unit 6.Control may be open-loop or closed-loop: e.g. the automated controls arecontrolled by means of an electrical energy source feedback and controlsignal 78 provided from sensors of the engine-generator such that if adifference between the output of a particular operation parameter and anassociated reference value is a certain amount then the input is changedaccordingly. The electrical energy source feedback and control signal 78may comprise information relating to aspects of the engine-generator,such as one of more of the following: angular velocity; choke; oillevel/temperature; water level/temperature; other operationalparameters.

In FIG. 3 a second embodiment of an electrical energy source 4 is shown,which is suited to agricultural environments. Herein the electricalenergy source 4 comprises a vehicle 16, such as a vehicle adapted foragricultural use (e.g. a tractor), which provides rotational drive froma power take-off shaft to a rotor of an electro-magnetic generator 18.Typically the power take-off shaft rotates at 540 rpm, and via a drivetrain drives the rotor to rotate at 1500-1800 rpm. The electro-magneticgenerator 18 is configured to convert the rotational energy to theunprocessed electrical energy 34, which is in turn supplied to theelectrical energy processing unit 6 for processing. Typically theelectrical energy supplied from the electro-magnetic generator 18 has110 Vrms-240 Vrms at 50-60 Hz. The electro-magnetic generator may beintegrated as part of the vehicle, and thus the vehicle generates theunprocessed electrical energy 34.

In a third embodiment the electrical energy source 4 comprises a batteryor a fuel cell. In this embodiment the unprocessed electrical energy 34that is supplied to the electrical energy processing unit 6 is a directcurrent. An example of a suitable battery is a 12 V-24 V unit as used inthe automotive industry. This embodiment is applicable to agriculturalor home environments.

In a fourth embodiment the electrical energy source 4 comprises an ACline supply, such as a mains supply of a commercial or domesticproperty. Accordingly, the line supply may be 110-120 Vrms AC or 220-240Vrms AC at 50-60 Hz. This embodiment is applicable to agricultural orhome environments.

Processed Electrical Energy Circuit

The processed electrical energy circuit 20 comprises a circuit totransmit the processed electrical energy from the electrical energyprocessing unit 6. The circuit comprises electrodes of the applicatorunit 8 and earth unit 74 and in use a treated plant and the ground. Theapplicator unit 8 and earth unit 74 will be described sequentially.

Applicator Unit

The applicator unit 8 is configured to receive processed electricalenergy 36 from the electrical energy processing unit 6 and to transmitsaid electrical energy to one or more plants preferably by means ofdirect contact therewith.

The applicator unit 8 comprises one or a plurality of applicatorelectrodes, wherein the/each applicator electrode is configured to applythe processed electrical energy 36 to the/each plant, preferably viadirect contact therewith. In an example comprising a plurality ofapplicator electrodes the applicator electrodes may be arranged inseries or in parallel or a combination thereof with respect to thereceived electrical energy. Moreover, the electrical energy processingunit 6 may supply a separate electrical energy output for each or agroup (i.e. 2 or more) of the plurality of applicator electrodes, forexample, there is a separate transformer or transformer winding for eachor the group of applicator electrode. In a similar fashion a singleelectrical energy processing unit 6 may supply one or a plurality ofapplicator units 8, e.g. the applicator units 8 are arranged in seriesor in parallel or a combination thereof with respect to the receivedelectrical energy or the electrical energy processing unit 6 has aseparate electrical energy output for each applicator unit 8.

The applicator electrode comprises an electrically conductive materiale.g. copper, zinc, bronze, brass, aluminium or steel. The applicatorelectrode may further comprise an insulating dielectric material, whichis operable to conduct the processed electrical energy 36 by capacitiveaction, such as an alumina or other ceramic, e.g. alumina or porcelainor a plastic such as PerspexR. The dielectric material is arranged withrespect to the electrically conductive material such that a treatedplant receives the processed electrical energy 36 substantially orentirely via the dielectric material, e.g. an entire outer surface ofthe electrically conductive material is coated with the dielectricmaterial or an exposed outer surface is coated. Typically, thedielectric material of the applicator electrode is a layer or coating,which is 0.5-2.5 mm thick. Advantageously, the dielectric material actsto reduce arcing. Moreover, the processed electrical energy 36 in theconductive material of the applicator electrode can be prevented frombeing in direct contact with a user. The processed electrical energy 36can be effectively conducted through the dielectric material at thehigh-frequency, i.e. above 18 kHz or more particularly above 20 or 25 or40 or 50 kHz.

In view of the above, it will be appreciated that the applicator unit 8may comprise various arrangements. Embodiments with applicator unit(s)adapted for wide area coverage (e.g. by means of one or a combination ofthe following: numerous applicator units; numerous applicatorelectrodes; applicator units with electrodes for wide-area coverage) aresuited to agricultural or commercial applications. Likewise, embodimentswith applicator unit(s) adapted for small area coverage (e.g. by meansof one or a combination of the following: single applicator units;single or multiple applicator electrodes; electrodes with small-areacoverage) are suited to private non-commercial applications. Wide areacoverage can be defined as comprising a ground treatment area of 50 cm²or 1 m² or more. Small area coverage can be defined as individual plantsor a ground treatment area of up to 5 cm² or up to 10 cm². Examples ofvarious applicator units 8 are discussed following.

In FIG. 4 a first embodiment of an applicator unit 8 is illustrated,which is generally applicable to private non-commercial environments.Herein the applicator unit 8 comprises an application head 22 and a body24, which are described sequentially.

The application head 22 is for transmission of the electrical energy toa plant, and to this end comprises the applicator electrode 26 fordirect contact therewith. The applicator electrode 26 can be shaped withvarious configurations, which are selected for the intended treatmentregimen, for example: a rod for sweeping through areas of dense plants;a hook-shape for separating plants. The applicator electrode may besubstantially rigid or compliant such that it is displaced duringtreatment.

The body 24 is for: connection of the applicator unit 8 to a chassis ofthe apparatus 2 in an example wherein the applicator unit 8 is fixed toa chassis of the apparatus; holding by a user in an example wherein theapplicator unit 8 is discrete from a chassis and is movableindependently therefrom. To this end the body 24 may comprise aconnection/holding portion 80 and an extension portion 28. Theconnection/holding portion 80 is for said connection/holding of theapplicator unit 8. The extension portion 28 provides an extendedposition of the head 22 with respect to the connection/holding portion80 for convenience of use. At a proximal end of the extension portion 28is arranged the connection/holding portion 80 and at a distal end isarranged the head 22. The connection/holding portion 80 and extensionportion 28 are preferably made of an insulating material, such as aceramic or plastic or rubber. Hence the extension portion 28 safelybridges the distance between the connection/holding portion 80 and thehead 22. In the example wherein the applicator unit 8 is intended forholding by a user, the applicator unit 8 may have connected thereto apart of or all of a user interface (discussed later on), accordingly oneor more of the features controlled by a user via the user interface maybe controlled at the applicator unit 8.

In FIG. 5 a second embodiment of an applicator unit 8 is illustrated,which is generally applicable to agricultural environments. Herein theapplicator unit 8 comprises a frame 82, which as shown may be formed oflateral and transverse members. The frame as shown may comprise acentral portion 84 and first and second side portions 86. The sideportions 86 can be pivotally or telescopically connected to the centralportion such that they can be moved between an operating position and astowed position for transit. The frame 82 can be supported by anagricultural vehicle 88, such as a tractor or a trailer. With such anexample a suitable size is: 3 m×1.2 m in width and length respectivelyfor the central portion; 1.5 m×1.2 m in width and length respectivelyfor the side portions. The frame 82 is typically formed from anelectrically conductive material, e.g. a metallic material such assteel. In this way the frame 82 in itself comprises the applicatorelectrode 26. The electrically conductive material is preferably hollowe.g. tube with a diameter of 12 mm.

Earth Unit

The earth unit 74 is configured to receive the processed electricalenergy 36 from the applicator unit 8 via a plant and the earth, and isconnected to the electrical energy source 4, generally via the energyprocessing unit 6 to provide a return path for the components thereinand to complete a circuit that has a load comprising a treated plant andthe earth. In use it is preferred that the earth electrode is arrangedproximate the applicator unit 8 to reduce power loss into the earth (andfor electrical safety). In a similar fashion to the applicator unit 8,the earth unit 74 may have connected thereto a part of or all of a userinterface 42. Accordingly one or more of the features controlled by auser via the user interface may be controlled at the earth unit 74.

The earth unit 74 comprises an earth electrode 76 of electricallyconductive material configured for electrical continuity with theground. The electrically conductive material may comprise a metal suchas copper, zinc, bronze, brass, aluminium or steel. Typically, the earthelectrode 76 is 0.5-20 mm thick depending of the application andspecific shape, e.g.: a 10-20 mm diameter rod or a 0.5-20 mm thick platefor the respective first and second embodiments discussed following.

In a first embodiment of the earth unit the earth electrode is in theform of an implement, which is configured to provide the return pathwhen inserted into the ground, for example the earth electrode is formedas a spike or rod.

In a second embodiment of the earth unit 74 the earth electrode 76 isconfigured to provide a return path when resting on the ground.Generally, the earth electrode comprises a large surface area to aidelectrical transmission. The earth electrode may comprise asubstantially flat outer surface configured to stably rest against theground, such as a plate or other suitable shape, e.g.: a circular plate,which may have diameter of 10-20 cm; a square plate, which may have aside length of 10-20 cm. An example of such an earth unit 74 is shown inFIG. 6 , wherein an electrically insulating outer 90 surrounds acircular plate shaped earth electrode 76, which has an optionalinsulating dielectric material 92 discussed following. Alternatively theearth electrode may comprise (or be arranged around an outer peripheryof) one or more rotary members, such as a wheel or roller, which isconfigured to rotate along the ground as the apparatus 2 is moved (suchan example is shown in FIG. 15 ).

The earth electrode of the first or second embodiment may furthercomprise an insulating dielectric material, which is operable to conductthe processed electrical energy 36 by capacitive action, such as analumina or other ceramic, e.g. alumina or porcelain or a plastic such asPerspex®. The dielectric material is arranged with respect to theelectrically conductive material such that the electrically conductivematerial receives the processed electrical energy 36 substantially orentirely via the dielectric material, e.g. an entire outer surface ofthe electrically conductive material is coated with the dielectricmaterial or an exposed outer surface (that is to be inserted in or reston the ground for the respective embodiments) is coated and optionally arim adjacent thereto. Typically, the dielectric material of the earthelectrode is a layer or coating, which is 0.5-2.5 mm thick.Advantageously, the processed electrical energy 36 in the conductivematerial of the earth electrode is prevented from being in directcontact with a user.

The second embodiment of the earth unit is particularly suited for usewith an electrical energy processing unit 6 that produces processedelectrical energy 36 waveforms with a frequency in the range of above 18or 20 or 25 or 40 or 50 kHz. This is because the processed electricalenergy 36 of this frequency can be relatively efficiently transmittedfrom the ground to the earth electrode without the need for insertioninto the ground. As the frequency is increased the efficiency of theearth electrode in receiving the processed electrical energy 36increases such that it may be made smaller and/or in embodiments thatcomprise the dielectric material the thickness thereof increased.

The second embodiment earth unit is advantageous in comparison to thefirst embodiment earth unit when, for example, treating plants at afirst location and a distant second location: the earth electrode of thefirst embodiment earth unit requires extraction from the ground at thefirst location and insertion into the ground in operational proximity tothe second location; comparatively the earth electrode of the secondembodiment earth unit can be displaced from the first location to thesecond location by sliding or rolling it along the ground, thusobviating the steps of extraction and insertion. This functionality isparticularly useful for applications wherein large areas of plants arerequired to be treated, for example, applications in an agriculturalenvironment, wherein the apparatus 2 may be mounted to a vehicle drivensystem that is continuously is moved over the ground. Moreover, whentreating certain ground, such as tarmac or hard-packed stone, it may notbe possible to insert the first embodiment earth unit into the ground,and thus achieve adequate earth continuity. However, adequate earthcontinuity may still be achieved with the second embodiment earth unitsince insertion is not essential.

The second embodiment earth unit when comprising an outer layer ofinsulating dielectric material, in comparison to the first embodimentearth unit, may be less effective in receiving the processed electricalenergy 36 since the said capacitive action results in a slight voltagedrop, however this can be compensated by increasing the voltage of theprocessed electrical energy 36.

Apparatus 2 to electrically control plant growth which use the secondembodiment earth unit may be combined with other configurationapplicator units, e.g. those that transmit the processed electricalenergy to a plant not by direct contact therewith such as a sparktransmission system as disclosed in JP H3-83534, and the relatedpublication: ‘Destruction of Weeds by Pulsed High-Voltage Discharges’,A. Mizuno, T. Tenma and N. Yamano, Toyohashi University of Technology,1990.

Electrical Energy Processing Unit

The electrical energy processing unit 6 is configured to: receive theunprocessed electrical energy 34, from the electrical energy source 4;process the unprocessed electrical energy 34 to the processed electricalenergy 36; supply the processed electrical energy 36 between theapplicator unit 8 and earth unit 74 for transmission to a plant. Ingeneral the aforesaid processing comprises processing to achieve thedesired form of processed electrical energy 36, e.g. via conversion oneor more of the: voltage; current; frequency; other optional aspects ofthe waveform.

The processed electrical energy 36 may comprise a periodic or aperiodicwaveform, i.e. a waveform that continuously repeats with the repeatingunits therein having a constant or a varying period, e.g. a pulsed wavewith a fixed duty cycle or a varying duty cycle. The shape of therepeating unit may be one of or a combination of one or more of thefollowing forms: sine wave; saw-tooth wave; triangular wave; squarewave; pulsed, e.g. DC pulsatile, half-wave rectified; other known form.The exact shape of the repeating unit may be an approximation of one ofthe aforesaid forms for reasons of distortion, e.g. overshoot/undershootand the associated ringing and settle time. The repeating unit may bepositive or negative or a combination thereof with respect to areference value, which is typically 0 V.

FIG. 7 shows a block diagram of the electrical energy processing unit 6according to the invention. The electrical energy processing unit 6 maybe considered to comprise at a second level of the apparatus 2: anoptional control circuit 40; a converter 38, which are describedsequentially.

The control circuit 40 typically comprises a processor and userinterface (examples of which are discussed following). The controlcircuit 40 is operable to control, by means of a control signal 52(which may be any suitable signal type, e.g. a digital, DC or ACsignal), the converter 38 to convert the unprocessed electrical energy34 to the desired form of processed electrical energy 36. The exactoperation of the control circuit 40 depends on the conversionconfiguration of the converter 38, e.g.: in an example wherein theconverter 38 is configured to convert only frequency (i.e. theunprocessed electrical energy 34 is supplied at the desired voltage) thecontrol circuit 40 may supply a control signal to an electricallyoperated chopper switch of the converter 38, the switch arranged inseries with the unprocessed electrical energy 34. Alternatively, in anexample wherein the converter 38 is configured to convert only voltageand current (i.e. the unprocessed electrical energy 34 is supplied atthe desired frequency and waveform) the control circuit 40 may supply acontrol signal to a variable transformer of the converter 38.Alternatively, the control circuit 40 may control via a control signalconverter 38 that comprises a charge pump or boost converter or othersuitable component.

In an example wherein the converter 38 provides a fixed operation on theunprocessed electrical energy (e.g. it comprises only a non-variabletransformer for voltage and current conversion) it will be appreciatedthat a control circuit 40 may be obviated. However, generally theelectrical energy processing unit 6 comprises a control circuit 40 whencontrol of the said converter 38 is required.

In a preferred example, which is illustrated in FIG. 8 , the controlcircuit 40 is operable to generate a control signal comprising awaveform signal 52; the converter 38 is operable to convert, using thesaid waveform signal 52, the unprocessed electrical energy 34 toprocessed electrical energy 36, which has a waveform that corresponds tothat of the waveform signal 52. In the said preferred example thecontrol circuit comprises: a waveform generation unit 48; an optionalprocessor 50; an optional user interface 42, which are describedsequentially.

The waveform generation unit 48 is operable to generate the waveformsignal 52, which may have various forms that are repetitive and can beperiodic or aperiodic, e.g. a pulsed wave with a fixed duty cycle or avarying duty cycle. The shape of the repeating unit of the waveform maybe one of or a combination of one or more of the following forms: sinewave; saw-tooth wave; triangular wave; square wave; pulsed, e.g. DCpulsatile, half-wave rectified; other known form. Moreover, the waveformsignal may be positive or negative or a combination thereof with respectto a reference value, which is typically 0 V. The waveform generationunit 48 may for example comprise: a pulse width modulator (PWM); anarbitrary waveform generator (AWG); function generator; other suitablesignal generator. The waveform generation unit 48 may be separate to orintegrated with the processor 50 i.e. as a peripheral thereof.

The processor 50 generally is operable to control the converter 38 bymeans of the control signal 52. In the preferred example, which isillustrated in FIG. 8 , the processor 50 is operable to control thewaveform signal 52 via control of the waveform generation unit 48. In anexample wherein the waveform generation unit 48 is configured to outputa fixed waveform signal 52, the processor 50 can be obviated. Typicallythe processor 50 controls the form of the waveform of the processedelectrical energy 36, e.g. via the form of the waveform signal 52,however the control element may be less sophisticated, e.g. on/off.

The processor 50 in a general example is operable to receive an input,for example, one or more of the following: commands from the userinterface 42 via a user interface signal 44; the electrical energysource feedback and control signal 78 from the electrical energy source4; a converter feedback signal 70 from the converter 38; unprocessedelectrical energy 34. The input is processed according to program code(and/or programmed logic) stored on a memory unit of the processor 50 todetermine an output. The output may be control via the control signal52, e.g. open or closed-loop control, of one or more of the followingaspects of the processed electrical energy 36: form; duty cycle, whichis typically in the range of 0.05-0.45 (e.g. for a pulsed waveform);on/off; amplitude (e.g. to maintain the peak voltage at a particularmagnitude for varying load); frequency; period; current; power; shape;other aspect. In the preferred example, which is illustrated in FIG. 8 ,the said control of the processed electrical energy 36 is typically viacontrol of the corresponding waveform signal 52, e.g. via a controlsignal 54 to the waveform generation unit 48 and other associated unitswhen present (such as a driver as discussed in the specific exampleslater on). The output may further be control of the unprocessedelectrical energy 34 from the electrical energy source 4 by open-loopcontrol or by closed-loop control by means of the electrical energysource feedback and control signal 78.

The processor 50 generally comprises memory, input and output systemcomponents, which are arranged as an integrated circuit, typically as amicroprocessor or a microcontroller. The processor 50 may comprise othersuitable integrated circuits, such as: an ASIC; a programmable logicdevice such as an FPGA; an analogue integrated circuit, such as acontroller. For such devices, where appropriate, the aforementionedprogram code can be considered programed logic or to additionallycomprise programmed logic. The processor 50 may also comprise aplurality of the aforementioned integrated circuits. An example isseveral integrated circuits arranged in communication with each other ina modular fashion e.g.: a slave integrated circuit to control the userinterface 42 in communication with a master integrated circuit tocontrol the waveform generation unit 48.

The processor 50 generally comprises a memory unit for storage of theprogram code and optionally data. The memory unit typically comprises: anon-volatile memory e.g. EPROM, EEPROM or Flash for program code andoperating parameter storage; volatile memory (RAM) for data storage. Thememory unit may comprise a separate and/or integrated (e.g. on a die ofthe processor) memory unit. The processor 50 may be idealised ascomprising a control unit and an arithmetic logic unit or a pluralitythereof, i.e. multiple processors.

The user interface 42 comprises hardware to enable a user to interfacewith the processor 50, by means of a user interface signal 44. A usermay be able to control one or more of the outputs of the processor 50via the user interface, e.g. the said aspects of the processedelectrical energy 36 including: optional high, medium and low powersettings (e.g. low power may be 50% of the high power and medium powermay be 75% of the high power); optionally a reset power setting.Moreover, in embodiments comprising a plurality of applicator units 8and/or applicator electrodes 26, the aforementioned aspects of theprocessed electrical energy 36 may be controlled via the user interface42 for the applicator units 8 and/or applicator electrodes individuallyor in groups. A user may further be able to control one or more of thefollowing aspects of the electrical energy source 4/unprocessedelectrical energy 34 via the user interface 42: on/off; voltage;current; other aspects that will depend on the particular embodiment ofthe electrical energy source 4.

The hardware of the user interface 42 may comprise any suitabledevice(s), e.g. one or more of the following: buttons, such as ajoystick button; LEDs; graphic or character LDCs; graphical screen withtouch sensing or screen edge buttons; on/off switch. The user interface42 can be formed as one unit or a plurality of discrete units, and maybe arranged remote from the other third level components of the controlcircuit 40, e.g. in apparatus 2 adapted for use in an agriculturalenvironment it may be arranged in the cabin of an agricultural vehicle.

The user interface signal 44 is transmitted between the user interface42 and the processor 50 by means of cabled media or wireless media or acombination thereof, e.g.: a wired connection, such as RS-232, USB, I²C,Ethernet define by IEEE 802.3; a wireless connection, such as wirelessLAN (e.g. IEEE 802.11) or near field communication (NFC) or a cellularsystem such as GPRS or GSM. For more sophisticated media the processor50 and user interface 42 can be operatively connected to (or comprisesas a peripheral) the relevant communication interfaces. The processor 50may be operatively connected to (or comprises as a peripheral) a webserver or a network router and the user interface 42 may comprise aprogram such as a web browser executed by a communication device such asa: PDA; tablet; laptop; smartphone; PC; or other suitable device.

The components that comprise the control circuit 40 are typicallypowered by the unprocessed electrical energy 34 from the electricalenergy source 4 following conversion to a suitable voltage, e.g. 10 VDC. They may alternatively be powered by a separate electrical energysource.

The converter 38 will now be discussed and, as illustrated in FIG. 7 ,is configured to: generally receive the control signal 52 from thecontrol circuit 40; receive the unprocessed electrical energy 34 fromthe electrical energy source 4; convert, generally using the controlsignal 52, the unprocessed electrical energy 34 to the desired form,e.g. via conversion one or more of the: voltage; current; frequency;other optional aspects of the waveform; transmit said processedelectrical energy 36 to the processed electrical energy circuit 20.

The converter 38 may have various configurations depending on its modeof operation, e.g.: in an example wherein the converter 38 convertsfrequency (i.e. the unprocessed electrical energy 34 is at the desiredvoltage) the converter 38 comprises a converter unit in the form of anelectrically operated chopper switch, the switch arranged in series withthe unprocessed electrical energy 34. Alternatively, in an examplewherein the converter 38 converts voltage and current (i.e. theunprocessed electrical energy 34 is at the desired frequency) theconverter 38 comprises a converter unit in the form of a variable ornon-variable transformer. In further examples the converter unit maycomprise a charge pump or boost converter or other suitable electricalcomponent.

In the preferred example, which is illustrated block form in FIG. 8 andschematically in FIG. 9 , the converter 38 comprises: a switching unit56; a converter unit 58, and is operable to convert voltage, current andfrequency, and other optional aspects to derive the desired the waveformof the processed electrical energy 36. The switching unit 56 andconverter unit 58 will be described sequentially.

The switching unit 56 is configured to receive the control signal 52and, using the control signal 52, switch the unprocessed electricalenergy 34 at a desired frequency through the converter unit 58.Accordingly, the switching unit 56 generally comprises an electricallyoperated switch, an example of which is one or more (e.g. a Darlingtonpair or other arrangement) transistor. The transistor is generallyarranged with: a base connected to the control signal 52; an emittergrounded; a collector connected to the unprocessed electrical energy 34via the converter unit 58, although various other arrangements arepossible. Other forms of electrically operated switch may be used, suchas a MOSFET, IGBT or triac.

The converter unit 58 is operable to receive the switched unprocessedelectrical energy 34 and to transform its voltage to a desired magnitudeto determine the processed electrical energy 36. Accordingly, theconverter unit 58 generally comprises: a step-up transformer 64 having aprimary winding arranged in series with the switched unprocessedelectrical energy 34; a secondary winding arranged in series with theapplicator unit 8 and earth unit 74, thereby defining a circuit comprisea treated plant.

The converter 38 may further comprise one or more sensor(s) 68 formonitoring and/or controlling aspects of the processed electrical energy36, for example, the voltage and/or current. The sensor(s) 68 provide aconverter feedback signal 70 (which may be any suitable signal type,e.g. a digital, DC or AC signal), to the processor 50, typically forclosed-loop control. As an alternative to use in closed-loop control (orin addition) the converter feedback signal 70 may be stored on thememory unit so that it may subsequently be analysed.

The electrical energy processing unit 6 is typically configured togenerate processed electrical energy 36 that has a waveform with a peakvoltage in the range of 1 kV to 30 kV: it may be specifically configuredor user controllable to generate a waveform with any peak voltagetherebetween. Generally, the voltage is about 4-8 kV.

The electrical energy processing unit 6 is typically configured togenerate processed electrical energy 36 that has a waveform that repeatscontinuously with a frequency of 18 kHz to 5 MHz: it may be specificallyconfigured or user controllable to generate a waveform that repeats withany frequency therebetween. Generally, the frequency is about 20-75 kHz.

As electrical current flows through a plant, the plant can be killed bythe current due to heat generated by the plant's resistance to electronflow. In more detail, as the current flows it damages the cellularstructure of the plant and water is released. The increased water hasthe effect of reducing the resistance: this allows more current to flowso more damage is done, reducing the resistance still further, so morecurrent flows and so on. The current therefore generally rises withtime. The initial current required to kill a particular plant will varyconsiderably depending on the type of plant, its moisture content, andthe moisture of the air, soil etc. The electrical energy processing unit6 is typically configured to generate processed electrical energy 36that has initial current of at least 10 mA, although typically a higherinitial current is used.

The electrical energy processing unit 6 is typically configured togenerate processed electrical energy 36 that has an initial power of atleast 5 W. The initial power may vary depending on the embodiment of theelectrical energy source 4 that the electrical energy processing unit 6is configured to operate with, e.g.: for the first or second embodimentthe initial power may be 3-6 kW for 3-5 kV; for the third embodiment theinitial power may be 500-2000 W for 2.5-4 kV; for the fourth embodimentthe initial power may be 2-3 kW for 2.5-4 kV. Generally, for apparatus 2intended for agricultural/commercial use the electrical energyprocessing unit 6 and electrical energy source 4 produce processedelectrical energy 36 with an initial power of 10-60 kW at 5-20 kV.Generally, for apparatus 2 intended for private non-commercial use, theelectrical energy processing unit 6 and electrical energy source 4produce an initial power of 100-3000 W at 2-5 kV.

The electrical energy processing unit 6 is typically configured togenerate processed electrical energy 36 that can kill a plant with atreatment time of at least 10 milliseconds. It will be appreciated thata small treatment time, such as 10 milliseconds will be applicable tosmall plants, whereas large plants will take longer, such as 5-6seconds.

The processed electrical energy 36 may be controlled by the processor 50in various ways, such as control over (or through) the load (comprisinga treated plant and the earth) of the: voltage; current; power, examplesof which will now be discussed.

The following examples of processed electrical energy 36 control may beapplied to apparatus 2 that generate lower frequency processedelectrical energy 36, such as processed electrical energy 36 with anyvoltage and frequency suitable for killing a plant, e.g. 50-60 Hz (asdisclosed in U.S. Pat. No. 4,338,743) up to the above preferred range(it will be appreciated that the above electrical energy processing unit6 could be configured to produce this processed electrical energy, e.g.by generation of the appropriate control signal 52). Moreover, thecontrol may be applied to apparatus 2 with other configurationapplicator units, e.g. those that transmit the processed electricalenergy to a plant without direct contact therewith, such as a sparktransmission system as disclosed in JP H3-83534, and the relatedpublication: ‘Destruction of Weeds by Pulsed High-Voltage Discharges’,A. Mizuno, T. Tenma and N. Yamano, Toyohashi University of Technology,1990.

Example 1: Control of Voltage Generally to Maintain a Constant VoltageOver the Load

As the load (i.e. the current drawn) between the applicator unit 8 andearth unit 74 decreases the voltage over the load generally increases.In a similar fashion, as the load between the applicator electrode 26 ofthe applicator unit 8 and earth unit 74 increases the voltage over theload generally decreases. Accordingly, the voltage of the processedelectrical energy 36 can be maintained at particular value or range(i.e. a range defined by a first and/or second predetermined value) byopen loop control or by closed loop control (e.g. by monitoring thevoltage of the processed electrical energy 36 using the converterfeedback signal 70). The voltage of the processed electrical energy 36can be increased in response to a decreasing voltage by increasing itsduty cycle (or amplitude) or decreased in response to an increasingvoltage by decreasing its duty cycle (or amplitude). In this way thevoltage is kept as high as possible to optimise the duration (e.g. thespeed) of the process.

As an example of this process: the voltage may be maintained at 2 kV or5 kV or 10 kV, including ±5% or 10% thereof.

Example 2: Control of Current Generally to Maintain a Constant CurrentThrough the Load

During treatment of a plant, the current through the plant generallyincreases due to the resistance of the plant decreasing as damage to thecellular structure occurs. Accordingly, the current of the processedelectrical energy 36 can be maintained at particular value or range(i.e. a range defined by a first and/or second predetermined value) byopen loop control or by closed loop control (e.g. by monitoring thecurrent of the processed electrical energy 36 using the converterfeedback signal 70). The current of the processed electrical energy 36can be increased in response to a decreasing current by increasing itsduty cycle (or amplitude) or decreased in response to an increasingcurrent by decreasing its duty cycle (or amplitude).

The aforementioned current control may only be applied to a graduallyincreasing current once it achieves one of the said predeterminedvalues.

In this way overload of the converter can be avoided. Moreover, thevoltage is kept as high as possible whilst the current is rising tooptimise the duration (e.g. the speed) of the process.

As an example of this process: for a 500 W unit configured to generateprocessed electrical energy 36 at 5 kV, once the processed electricalenergy 36 achieves a current of 0.1 A, the voltage of the processedelectrical energy 36 is reduced, to maintain the current of 0.1 A or 0.1A±5%.

Example 3: Control of Power to Maintain Generally a Constant PowerThrough the Load

During treatment of a plant, the current through the plant generallyincreases due to the resistance of the plant decreasing as damage to thecellular structure occurs. Accordingly, the power of the processedelectrical energy 36 can be maintained at particular value or range(i.e. a range defined by a first and/or second predetermined value) byopen loop control or by closed loop control (e.g. by monitoring thecurrent and voltage of the processed electrical energy 36 using theconverter feedback signal 70). The voltage of the processed electricalenergy 36 can be increased in response to a decreasing current byincreasing its duty cycle (or amplitude) or decreased in response to anincreasing current by decreasing its duty cycle (or amplitude).

The aforementioned power control may only be applied to a graduallyincreasing power once it achieves one of the said predetermined values.

In this way overload of the converter can be avoided. Moreover, thevoltage is kept as high as possible whilst the current is rising tooptimise the speed of the process.

As an example of this process: once the processed electrical energy 36achieves a current of 0.1 A, the voltage of the processed electricalenergy 36 is reduced to maintain the power at a first predeterminedamount of 500 W or 500 W±5%; as the current continues to increase thevoltage is reduced to maintain 500 W or 500 W±5%, e.g. as the currentrises to 0.2 A the voltage is reduced to 2.5 kV, and at 0.5 A thevoltage is reduced to 1 kV.

Specific Example Circuits for the Electrical Energy Processing Unit

It will be appreciated that the aforementioned circuits of theelectrical energy processing unit 6 may comprise various electricalcomponents, some specific examples of which are provided following.

Embodiment 1: Pulse Width Modulated Forward Convertor

A first embodiment of the electrical energy processing unit 6 is shownin FIG. 10 , wherein the control circuit 40 comprises a processor 50that is a microprocessor and a waveform generation unit 48 that is apulse width modulator (PWM). The microprocessor controls the PWM bymeans of control signal 54 that is decoded by the PWM and converted to asquare wave. The duty cycle and frequency of the square wave arecontrolled by the microprocessor via the control signal 54. The controlsignal 54 may be any suitable signal type, e.g. a digital, DC or ACsignal. The PWM outputs the control signal 52 to the converter 38.

The converter 38 comprises a switching unit 56 that is a MOSFET, whichis arranged with: the gate connected to the control signal 52 from thePWM; the source grounded; the drain connected to the unprocessedelectrical energy 34. The converter 38 further comprises a converterunit 58, which has a transformer 64 with a primary and secondary windingarranged as described in the general example above and a reset windingto rid a core of the transformer of stored energy during the off cycleto avoid/reduce saturation. The converter 38 has sensors 68 consistingof a current sensor in series with the load and a divider arranged overthe load for voltage measurement. Accordingly a converter feedbacksignal 70 from the sensors 68 provides voltage and current informationto the processor 50.

The control signal 52 switches the MOSFET 56 to effect switching of theunprocessed electrical energy 34 across the primary winding of thetransformer 64, which is transformed at the secondary winding to theprocessed electrical energy 36.

The first embodiment of the electrical energy processing unit 6 isgenerally suitable for operation at less than 300 Watts.

Embodiment 2: Linear Amplifier

A second embodiment of the electrical energy processing unit 6 is shownin FIG. 11 , wherein the control circuit 40 comprises: a processor 50that is a microprocessor; a waveform generation unit 48; an op-amp andassociated driver. The microprocessor 50 controls the driver by means ofthe control signal 54. The waveform generation unit 48 outputs a controlsignal to the driver, which may for example be a sine wave (or other oneof the aforementioned waves). Aspects of the control signal (e.g. formand frequency) output from the waveform generation unit 48 may be fixedor controllable by the microprocessor 50. The driver transfers thecontrol signal to the non-inverting input of the op-amp where it isamplified to the required level, as will be discussed.

The converter 38 comprises a switching unit 56 that is a NPN transistorand a PNP transistor, which are arranged with: the bases connected inparallel to the control signal 52 from the op-amp; the emittersconnected to each other and to the primary winding of the transformer;the collector of the NPN transistor connected to the positive powersupply of the op-amp; the collector of the PNP transistor connected tothe negative power supply of the op-amp. The converter 38 furthercomprises a converter unit 58, which has a transformer 64 with a primaryand secondary winding arranged as described in the general exampleabove. The converter 38 has sensors 68 consisting of a current sensor inseries with the load and a divider arranged over the load for voltagemeasurement. The current sensor 68 is connected to the microprocessor 50such that the converter feedback signal 70 provides current and voltageinformation thereto. The voltage sensor 68 is connected to the invertinginput of the op-amp such that the converter feedback signal 70 providesvoltage information thereto.

The control signal 52 switches the NPN and PNP transistors when positiveor negative respectively to effect switching of the unprocessedelectrical energy 34 across the primary winding of the transformer 64 inaccordance with the control signal 52. As shown in FIG. 12 a-b , theprocessed electrical energy 36 at the secondary winding of thetransformer 64 is substantially an amplification of the control signal52. More particularly, FIG. 12 a shows the amplification of a squarecontrol signal 52 and FIG. 12 b shows the amplification of a sinecontrol signal 52. The voltage feedback of the converter feedback signal70 to the inverting input of the op-amp enables the maintaining by theop-amp of a constant voltage as the load (e.g. the resistance of atreated plant) varies. The microprocessor may comprise program code toeffect control of the driver to maintain or decrease the gain of theop-amp in accordance with the current feedback of the converter feedbacksignal 70 to the microprocessor.

The second embodiment of the electrical energy processing unit 6 isgenerally suitable for operation at less than 1500 Watts.

Embodiment 3: Push-Pull System

A third embodiment of the electrical energy processing unit 6 is shownin FIG. 13 , wherein the control circuit 40 comprises a processor 50that is a microprocessor and a waveform generation unit 48 that is acontroller with an integrated waveform generator. The microprocessor 50controls the controller by means of the control signal 54 that isdecoded by the controller to control the control signal 52. Thecontroller is configured to generate a control signal 52 that comprisesa first and second channel that is supplied to the respective first andsecond transistors of the converter 38. The first and second channelwaveforms are both square waves, the duty cycle and frequency of whichis controlled by the microprocessor via the control signal 54. Thecontrol signal 54 may be any suitable signal type, e.g. a digital, DC orAC signal.

The converter 38 comprises a switching unit 56 that comprises a firstand second NPN transistor, which are arranged with: the base of thefirst transistor connected to the first channel control signal 52 fromthe controller; the base of the second transistor connected to thesecond channel control signal 52 from the controller; the emittersgrounded; the collector of the first transistor connected to firstprimary windings of the transformer 64; the collector of the secondtransistor connected to second primary windings of the transformer 64.

The converter further comprises a converter unit 58, which comprises thetransformer 64 with a secondary winding arranged as described in thegeneral example above. The unprocessed electrical energy 34 is connectedto both primary windings of the transformer. The primary windings arearranged such that their energising causes flux to flow in the core inrespective first and second opposed directions. Accordingly, thetransistors are sequentially switched by the first and second channelcontrol signals to effect the transformation of processed electricalenergy 36 that corresponds to the sum of the first channel controlsignal with the out of phase second channel control signal.

The converter 38 has sensors 68 consisting of a current sensor arrangedin series with the load and a divider arranged over the load for voltagemeasurement. Accordingly a converter feedback signal 70 from the sensors68 provides voltage and current information to the processor 50.

The third embodiment of the electrical energy processing unit 6 isgenerally suitable for operation at less than 1000 Watts.

Embodiment 4: Full Bridge Converter

A fourth embodiment of the electrical energy processing unit 6 is shownin FIG. 14 , wherein the control circuit 40 comprises a processor andwaveform generator integrated as a controller. The controller isconfigured to generate a control signal that comprises a first, second,third and fourth channel that is supplied to the respective first,second, third and fourth transistors of the converter. The first,second, third and fourth channel waveforms are all square waves, theduty cycle and frequency of which is controlled by the controller.

The converter comprises a switching unit 56 that comprises the first T1,second T2, third T3 and fourth T4 NPN transistors. The transistors arearranged to in series pairs: T1 and T2; T3 and T4. The converter furthercomprises a converter unit 58, which comprises a transformer 64 with asecondary winding arranged as described in the general example above.The primary winding of the transformer is connected across the junctionsof the series pairs. The controller supplies the control signal thatsequentially switches opposed transistor pairs: T1 and T3; T2 and T4.The current therefore travels via the said opposed pairs to effect analternating current across the primary winding. Accordingly, theprocessed electrical energy 36 transformed corresponds to the sum of thefirst (and third) channel control signal with the out of phase second(and fourth) channel control signal.

The converter 38 has sensors 68 consisting of a current sensor arrangedin series with the load and a divider arranged over the load for voltagemeasurement. Accordingly a converter feedback signal 70 from the sensors68 provides voltage and current information to the controller.

The fourth embodiment of the electrical energy processing unit 6 isgenerally suitable for operation at above 1000 Watts.

General Example of Apparatus for Agriculture

FIG. 15 shows and overall example of the apparatus 2 when adapted foragriculture, wherein: the electrical energy source 4 comprises a vehicleaccording to the second embodiment; the electrical energy processingunit 6 is arranged on a towed vehicle; a plurality of applicator units 8extend from the vehicle; the earth unit 74 comprises a rotary memberaccording to the second embodiment.

Experimental Results

Experimental results were obtained by the application of electricalenergy according to the invention and the prior art to small samples of5-10 French Marigold, each sample was grown under the same conditionsfor 8 weeks. In particular: the voltage (peak) was varied from 3 kV-6 kVin 1 kV increments; the frequency was varied generally from 5 kHz-50 kHzin 5 kHz increments; the electrical energy was applied for 1 second. Thesubsequent response of the plant was observed for the period of 4 days.

Referring to FIG. 16 it can be seen that although there is a largeamount of variation in the experimental results (which would be improvedby an increased sample size) the kill efficacy (in %) is maintainedabove around 18-25 kHz. It is expected that if the sample size/range ofplants tested were to be increased, the potential advantage ofhigh-frequency would be more pronounced. At around 3 kV, which may beconsidered a threshold voltage, there is insufficient electrical energyto reliably kill the sample at all frequencies. A method of treatment ofa plant may therefore comprise establishing a threshold voltage. Themethod may also comprise determining a treatment time. The thresholdvoltage and time may be determined from experimental data, i.e. adatabase, and/or predicted.

LIST OF REFERENCES

-   2 Apparatus to control plant growth-   4 Electrical energy source-   34 Unprocessed electrical energy

Embodiment 1

-   10 Internal combustion engine-   12 Electro-magnetic generator-   14 Controls

Embodiment 2

-   16 Vehicle-   18 Electro-magnetic generator-   6 Electrical energy processing unit-   36 Processed electrical energy-   38 Converter-   56 Switching unit-   58 Converter unit-   64 Transformer-   68 Sensor-   70 Converter feedback signal-   40 Control circuit-   48 Waveform generation unit-   52 Control signal-   50 Processor-   78 Electrical energy source feedback and control signal-   54 Control signal-   42 User interface-   44 User interface signal-   20 Processed electrical energy circuit-   74 Earth unit-   76 Earth electrode-   90 Electrically insulating outer-   92 Insulating dielectric material-   8 Applicator unit

Embodiment 1

-   22 Head-   26 Applicator electrode-   24 Body-   80 Mounting/holding portion-   28 Extension portion

Embodiment 2

-   82 Frame (applicator electrode 26)-   84 Central portion-   86 Side portion-   88 Vehicle

What is claimed is:
 1. An apparatus to electrically kill a plant or atleast attenuate plant growth, the apparatus comprising: an electricalenergy processing unit comprising a converter operable to receiveunprocessed electrical energy from an electrical energy source, toconvert the unprocessed electrical energy to processed electrical energyhaving an electrical current and to transmit the processed electricalenergy between an applicator electrode of an applicator unit and anearth electrode of an earth unit; the applicator unit comprising theapplicator electrode, wherein the applicator electrode comprises anelectrically conductive material, the applicator unit being electricallycoupled to the converter of the electrical energy processing unitwherein the applicator unit is operable to receive the processedelectrical energy and to apply the processed electrical energy directlyto at least a portion of a plant that extends above the ground; and theearth unit comprising the earth electrode, wherein the earth electrodecomprises an electrically conductive material, the earth unit beingelectrically coupled to the converter, wherein the earth unit isoperable to receive the processed electrical energy transmitted from theapplicator unit through a load comprising the plant, and wherein theearth electrode comprises a surface that is configured so as toelectrically couple the earth unit to the ground; and wherein theapplicator electrode is configured for direct transmission of theprocessed electrical energy to at least part of the plant above groundsuch that the electrical current travels through the at least part ofthe plant above ground as part of a circuit and the electrical currentreturns to the earth electrode through the ground, wherein the processedelectrical energy comprises a waveform with a frequency and with a peakvoltage of at least 1 kV and with an electrical current of at least 10mA rms; wherein the electrical energy processing unit further comprisesa control circuit operable to control the converter to convert theunprocessed electrical energy to the processed electrical energy,wherein the control circuit is configured to control an aspect of theprocessed electrical energy comprising one or a combination of thevoltage, current, and power, the said aspect controlled to be:maintained substantially at a predetermined value; or below or above apredetermined value; or within a particular range which is determined bya first predetermined value and second different predetermined value;wherein the control circuit is configured to control the said aspect ofthe processed electrical energy by controlling an amplitude and/or dutycycle or period of the processed electrical energy.
 2. The apparatus ofclaim 1, wherein the electrical energy processing unit is configured toproduce processed electrical energy that comprises a power of at least 5W.
 3. The apparatus of claim 1, wherein the electrical energy processingunit is configured to produce processed electrical energy that isoperable to kill a plant or at least partially attenuating plant growthwith a treatment time of at least 10 milliseconds.
 4. The apparatus ofclaim 1, wherein the converter comprises at least one sensor, thecontrol circuit being operatively connected to the sensor to receivetherefrom a converter feedback signal, the converter feedback signalcomprising information to monitor said aspect of the processed electricenergy wherein the control circuit is configured to provide control ofthe said aspect of the processed electrical energy based on theconverter feedback signal.
 5. The apparatus of claim 1, wherein theearth electrode comprises a substantially flat surface configured toreceive the processed electrical energy when resting on a surface of theground.
 6. The apparatus of claim 1, wherein the applicator unitcomprises a plurality of applicator electrodes.
 7. A method of using anapparatus to electrically kill a plant or at least attenuate plantgrowth, the method comprising the steps of: obtaining an apparatuscomprising an electrical energy processing unit, an applicator unitcomprising an applicator electrode, and an earth unit comprising anearth electrode, wherein the electrical energy processing unitcomprising a converter operable to receive unprocessed electrical energyfrom an electrical energy source, to convert the unprocessed electricalenergy to processed electrical energy having an electrical current andto transmit the processed electrical energy between the applicatorelectrode of the applicator unit and the earth electrode of the earthunit, wherein each of the applicator unit and the earth unit iselectrically coupled to the converter, and wherein each of theapplicator electrode and the earth electrode comprises an electricallyconductive material; directly contacting a portion of a plant thatextends above the ground with the applicator electrode; disposing asurface of the earth electrode substantially planar to a surface of theground or into the ground so as to electrically couple the earth unit tothe ground; supplying processed electrical energy directly to the plantwith the apparatus, wherein the processed electrical energy comprises awaveform with a frequency and with a peak voltage of at least 1 kV andwith an electrical current of at least 10 mA rms, wherein the applicatorelectrode directly transmits the processed electrical energy to theportion of the plant that extends above the ground such that theelectrical current travels through the at least part of the plant aboveground as part of a circuit and the electrical current returns to theearth electrode through the surface of the ground; and controlling anaspect of the processed electrical energy comprising one or acombination of the voltage, current, and power, the said aspectcontrolled to be: maintained substantially at a predetermined value; orbelow or above a predetermined value; or within a particular range,which is determined by a first predetermined value and second differentpredetermined value; and wherein the control circuit is configured tocontrol the said aspect of the processed electrical energy bycontrolling an amplitude and/or duty cycle or period of the processedelectrical energy.
 8. The method of claim 7, wherein the surface of theearth electrode is configured to receive the processed electrical energywhen resting on a surface of the ground, and wherein the method furthercomprises the step of: moving the earth electrode of the earth unitalong the surface of the ground whilst maintaining electrical continuitybetween the earth unit and the surface of the ground so as toelectrically kill or at least attenuate growth of a first plant locatedat a first location and a second plant located at a second location. 9.The method of claim 7, wherein the surface of the earth electrodedisposed substantially planar to a surface of the ground is not insertedinto the ground.